Polymer molding materials are widely used to make a wide variety of materials, including for example various display devices. It is often desirable and/or necessary to provide an anti-reflective layer or textured surface on such display devices to inhibit reflected light to ensure satisfactory visibility. Various methods have been suggested for producing such anti-reflective layers, including, for example, using vacuum deposition or sputtering to provide a multi-layered film composed of dielectrics having different refractive indices.
It has also been suggested to use a porous alumina master having an arrangement of depressions or pores corresponding to projections to be imparted to the surface of the polymer molding material to create an anti-reflective layer in polymeric molding materials.
The depressions or pores formed in the porous alumina master for forming corresponding projections on the surface of the polymer molding material typically have an extremely low period as compared with the wavelength of light, and for example, may have a depth of about ¼ the wavelength to adequately attenuate reflectance in the visible light range.
U.S. Patent Publication No. 2007/0289874 to Masuda et al., the subject matter of which is herein incorporated by reference in its entirety describes a method of producing a non-reflective polymer film by repeating anodic oxidation at about the same formation voltage and pore diameter enlargement treatment, and using anodic oxidized porous alumina, to which a tapered shape has been, imparted in which pore diameter continuously changes, as a mold. The anodized porous alumina surface is used as a mold, or a stamper for imparting projections to the surface of a polymeric molding material to create an anti-reflective layer therein.
After carrying out anodic oxidation for a predetermined amount of time to form pores having a desired depth, pore diameter enlargement treatment is carried out by immersing the mold in a suitable acidic solution. Subsequently, by carrying out anodic oxidation at a formation voltage approximately equal to that of the anodic oxidation previously carried out, pores having a smaller diameter as compared with the first stage are formed. Subsequently, when anodic oxidation and pore diameter enlargement treatment are repeated, as a result of carrying out anodic oxidation at about the same formation voltage as the previous anodic oxidation, the pores to be formed are formed perpendicular to the direction of film thickness, thereby making it possible to form pores having a regular tapered shape. By repeating this procedure, an oxidized porous alumina substrate having pores with a tapered shape can be obtained.
The inventors of the present invention have determined that cylindrical pores, i.e., those have straight sides versus tapered, provide just as good a result as tapered pores for optical performance. One of the reasons that tapered pores have been preferred to cylindrical pores is that they have been significantly easer to obtain release from in standard pattern transfer processes.
Based thereon, the present invention relates in part to an anti-reflective layer (anti-reflective film) formed on the surface of a polymer molding material which reduces reflection in the visible light range and a production method thereof. In addition, the present invention relates generally to a master, preferably of alumina, having cylindrical pores disposed therein for forming a desired texture in the surface of the polymeric molding material, such as an anti-reflective layer and a production method thereof.
The present invention also relates generally to the production of porous alumina molds having cylindrical pores disposed therein utilizing a series of electrochemical steps, wherein the porous alumina mold is treated with a release coating to facilitate removal of polymer molding material from the porous alumina mold.